Several different devices have been utilized in the production of fuel cell structures such as electrode substrates and separator plates. One apparatus utilizes a roller and a conveyer belt to form composite mixtures into composite substrates. A composite mixture is deposited upon the conveyer belt and is fed underneath the roller which turns continually in an opposite direction to that of the conveyor belt. This process meters and compacts the composite mix. However, this method is characterized by voids, cracks, inhomogeneities and other imperfections that appear in the finished composite sheet. In addition to a localized reduction in strength and incipient crack formation, these defects cause reduced cell performance, specifically they result in, for example, diffusion differences, acid transfer problems and maldistribution of gas flows. These defects are especially apparent when the composites are comprised of fibrous mixtures having long length fibers.
When long length fibers are combined with resin, heated and cured, the resins will bind the fibers into an interlocking matrix which has the strength, rigidity, porosity and other properties needed in fuel cell structures. However, the very properties which the fibers impart to the finished fuel cell structure cause them to interlock, form aggregates, and resist movement during handling of the dry fiber/powder mixtures. This causes difficulty in depositing the fibrous mixtures into molds, or even onto flat plates in the production of fuel cell structures.
Accordingly, there is a constant search in this art for apparatuses and methods for making composite sheets which overcome such problems.